Apparatus for forming a resin impregnated flexible graphite sheet

ABSTRACT

A flexible graphite sheet exhibiting enhanced isotropy is provided. In addition, an apparatus, system and method for continuously producing a resin-impregnated flexible graphite sheet is also provided.

RELATED APPLICATION

This application is a divisional of our prior U.S. patent applicationSer. No. 09/548,118 entitled “Flexible Graphite Article and Method ofManufacture” filed Apr. 12, 2000, now U.S. Pat. No. 6,432,336.

TECHNICAL FIELD

The present invention relates to planar flexible graphite articles, suchas flexible graphite sheet, and to a system and method for continuouslyproducing such articles. More particularly, the present inventionrelates to flexible graphite sheet material that exhibits enhancedisotropy with respect to thermal and electrical conductivity and fluiddiffusion, as well as to a method for producing the sheet.

BACKGROUND OF THE INVENTION

Graphites are made up of layer planes of hexagonal arrays or networks ofcarbon atoms. These layer planes of hexagonally arranged carbon atomsare substantially flat and are oriented or ordered so as to besubstantially parallel and equidistant to one another. The substantiallyflat, parallel equidistant sheets or layers of carbon atoms, usuallyreferred to as basal planes, are linked or bonded together and groupsthereof are arranged in crystallites. Highly ordered graphites consistof crystallites of considerable size: the crystallites being highlyaligned or oriented with respect to each other and having well orderedcarbon layers. In other words, highly ordered graphites have a highdegree of preferred crystallite orientation. It should be noted thatgraphites possess anisotropic structures and thus exhibit or possessmany properties that are highly directional, e.g., thermal andelectrical conductivity and fluid diffusion. Briefly, graphites may becharacterized as laminated structures of carbon, that is, structuresconsisting of superposed layers or laminae of carbon atoms joinedtogether by weak van der Waals forces. In considering the graphitestructure, two axes or directions are usually noted, to wit, the “c”axis or direction and the “a” axes or directions. For simplicity, the“c” axis or direction may be considered as the direction perpendicularto the carbon layers. The “a” axes or directions may be considered asthe directions parallel to the carbon layers or the directionsperpendicular to the “c” direction. The natural graphites suitable formanufacturing flexible graphite possess a very high degree oforientation.

As noted above, the bonding forces holding the parallel layers of carbonatoms together are only weak van der Waals forces. Graphites, especiallynatural graphites, can be treated so that the spacing between thesuperposed carbon layers or laminae can be appreciably opened up so asto provide a marked expansion in the direction perpendicular to thelayers, that is, in the “c” direction and thus form an expanded orintumesced graphite structure in which the laminar character of thecarbon layers is substantially retained.

Natural graphite flake which has been expanded and more particularlyexpanded so as to have a final thickness or “c” direction dimensionwhich is at least about 80 or more times the original “c” directiondimension can be formed without the use of a binder into cohesive orintegrated sheets, e.g., webs, papers, strips, tapes, or the like. Theformation of graphite particles which have been expanded to have a finalthickness or “c” dimension which is at least 80 times the original “c”direction dimension into integrated sheets by compression, without theuse of any binding material is possible. It is believed that this is dueto the excellent mechanical interlocking, or cohesion that is achievedbetween the voluminously expanded graphite particles.

In addition to flexibility, the sheet material, as noted above, has alsobeen found to possess a high degree of anisotropy with respect tothermal and electrical conductivity and fluid diffusion, comparable tothe natural graphite starting material due to orientation of theexpanded graphite particles substantially parallel to the opposed facesof the sheet resulting from very high compression, such as rollpressing. Sheet material thus produced has excellent flexibility, goodstrength and a very high degree of orientation.

Briefly, the process of producing flexible, binderless anisotropicgraphite sheet material comprises compressing or compacting under apredetermined load and preferably in the absence of a binder, expandedgraphite particles which have a “c” direction dimension which is atleast 80 times that of the original particles so as to form asubstantially flat, flexible, integrated graphite sheet. The expandedgraphite particles are generally worm-like or vermiform in appearance,and once compressed, will maintain the compression set and alignmentwith the opposed major surfaces of the sheet. The density and thicknessof the sheet material can be varied by controlling the degree ofcompression. The density of the sheet material can be within the rangeof from about 5 pounds per cubic foot to about 125 pounds per cubicfoot. The flexible graphite sheet material exhibits an appreciabledegree of anisotropy due to the alignment of graphite particles parallelto the major opposed, parallel surfaces of the sheet, with the degree ofanisotropy increasing upon roll pressing of the sheet material toincreased density. In roll pressed anisotropic sheet material, thethickness, i.e. the direction perpendicular to the opposed, parallelsheet surfaces comprises the “c” direction and the directions rangingalong the length and width, i.e., along or parallel to the opposed,major surfaces comprises the “a” directions and the thermal, electricaland fluid diffusion properties of the sheet are very different, byorders of magnitude, for the “c” and “a” directions.

This very considerable difference in properties, i.e., anisotropy, whichis directionally dependent, can be disadvantageous in some applications.For example, in gasket applications where flexible graphite sheet isused as the gasket material and in use is held tightly between metalsurfaces, the diffusion of fluid like gases or liquids occurs morereadily parallel to and between the major surfaces of the flexiblegraphite sheet. It would, in most instances, provide for greater gasketperformance, if the resistance to fluid flow parallel to the majorsurfaces of the graphite sheet (“a” direction) were increased, even atthe expense of reduced resistance to fluid diffusion flow transverse tothe major faces of the graphite sheet (“c” direction). With respect toelectrical properties, the resistivity of anisotropic flexible graphitesheet is high in the direction transverse to the major surfaces (“c”direction) of the flexible graphite sheet, and very substantially lessin the direction parallel to and between the major faces of the flexiblegraphite sheet (“a” direction). In applications such as seals or othercomponents (such as fluid flow field plates or gas diffusion layers) offuel cells, it would be of advantage if the electrical resistancetransverse to the major surfaces of the flexible graphite sheet (“c”direction) were decreased, even at the expense of an increase inelectrical resistivity in the direction parallel to the major faces ofthe flexible graphite sheet (“a” direction).

With respect to thermal properties, the thermal conductivity of aflexible graphite sheet in a direction parallel to the upper and lowersurfaces of the flexible graphite sheet is relatively high, while it isrelatively very low in the “c” direction transverse to the upper andlower surfaces. At times, and in certain applications, such as thermalinterfaces, it may be desirable to increase the thermal conductivity ofthe sheet in the “c” direction.

In some applications, it is important to incorporate additives in theflexible graphite sheet in order to achieve corrosion resistance and toimpregnate the flexible graphite sheet with resins and/or other materialto increase the strength and water resistance of the flexible graphitesheet. Also, it is important at times to provide such additives in thecourse of processing the natural graphite into flexible graphite.

These foregoing situations are accommodated by the present invention.

SUMMARY OF THE INVENTION

In accordance with the present invention, a flexible graphite article inthe form of a sheet having opposed, relatively planar, major surfaces isprovided. The article is formed of particles of expanded (or exfoliated)graphite, an optically detectable portion of which, at magnifications of100× or less, are substantially unaligned with the opposed planar majorsurfaces of the flexible graphite article. Preferably, at least aportion of the unaligned particles are transverse to the opposed majorsurfaces of the article. The flexible graphite article is characterizedby having decreased electrical resistivity and increased thermalconductivity in a direction transverse to the opposed planar majorsurfaces of the flexible graphite sheet and increased resistance tofluid flow in a direction parallel to the opposed planar major faces ofthe flexible graphite sheet. The flexible graphite sheet, with orwithout additives and/or impregnants, can be mechanically altered, suchas by embossing, die molding and cutting to form components forelectrochemical fuel cells, gaskets and heat conducting and heatresistant articles.

The present invention also includes an apparatus, system and method forproducing flexible graphite sheet articles, such as those havingdecreased electrical resistivity and increased thermal conductivity in adirection transverse to the opposed planar major surfaces of theflexible graphite sheet and increased resistance to fluid flow in adirection parallel to the opposed planar major faces of the flexiblegraphite sheet.

The inventive method comprises reacting raw graphite particles with aliquid intercalant solution to form intercalated graphite particles;exposing the intercalated graphite particles to a temperature of atleast about 700° C. to expand the intercalated graphite particles toform a stream of exfoliated graphite particles; continuously compressingthe stream of exfoliated graphite particles into a continuous coherentself-supporting mat of flexible graphite; continuously contacting theflexible graphite mat with liquid resin and impregnating the mat withliquid resin; and continuously calendering the flexible graphite mat toincrease the density thereof to form a continuous flexible graphitesheet having a density of from about 5 to about 125 lbs/ft³ and athickness of from about 1.0 to 0.003 inches.

The method also advantageously includes mechanically deforming a surfaceof the continuous flexible graphite sheet to provide a series ofrepeating patterns on a surface of the flexible graphite sheet or theremoval of material from the flexible graphite sheet in a series ofrepeating patterns and vaporizing at least some of the solvent from theresin prior to mechanically deforming a surface of the continuousflexible graphite sheet.

As noted, the present invention also includes an apparatus for thecontinuous production of resin-impregnated flexible graphite sheet,comprising a reactor vessel for containing as reactants graphiteparticles in mixture with a liquid intercalant solution to formintercalated graphite particles; an expansion chamber in operativeconnection with the reactor vessel, the interior of the expansionchamber being at a temperature of at least about 700° C. (and preferablyenclosing an open flame), such that passing intercalated graphiteparticles from the reactor vessel to the expansion chamber causesexpansion of the intercalated graphite particles to form exfoliatedgraphite particles; a compression station positioned to receiveexfoliated graphite particles for compressing such particles into acoherent self-supporting mat of flexible graphite; an impregnationchamber for contacting the flexible graphite mat with liquid resin andimpregnating the mat with the liquid resin; a calender mill disposed toreceive the flexible graphite mat for increasing the density of the matto form a continuous flexible graphite sheet preferably having a densityof from about 5 to about 125 lbs/ft³ and a thickness of no more thanabout 1.0 inches, more preferably about 1.0 to about 0.003 inches.

The inventive apparatus also preferably includes a device formechanically deforming a surface of the continuous flexible graphitesheet to provide a series of repeating patterns on a surface of theflexible graphite sheet or the removal of material from the flexiblegraphite sheet in a series of repeating patterns. It furtheradvantageously has an oven for receiving the mat from the device formechanically deforming a surface of the continuous flexible graphitesheet, to cure the resin with which the continuous flexible graphitesheet is impregnated.

In a particular embodiment of the invention, a system for the continuousproduction of surface patterned, resin-impregnated flexible graphitesheet is presented. The system includes:

(i) a reactor vessel for containing as reactants raw natural graphiteflake-like particles in mixture with sulfuric and nitric acids;

(ii) an acid containing vessel communicating with said reactor vesselfor the introduction of a mixture of sulfuric and nitric acid into saidreactor vessel;

(iii) a graphite particle containing vessel for the introduction ofgraphite particles into the reactor vessel;

(iv) a first additive containing vessel communicating with said reactorvessel for the introduction of intercalation enhancing materials, acidsor organic chemicals;

(v) a wash vessel containing water communicating with the reactor vesselto receive reaction product in the form of acid intercalated graphiteparticles and remove acid from the surface of the acid intercalatedgraphite particles and a portion of the mineral impurities contained inthe natural graphite particles introduced into the reactor vessel;

(vi) a drying chamber for drying washed acid intercalated graphiteparticles;

(vii) conduit means extending from said wash vessel to said dryingchamber for passing washed acid intercalated graphite particles from thewash vessel to the drying chamber;

(viii) a second additive containing vessel communicating with theconduit means of (vii) for adding pollution reducing chemicals to thewashed, intercalated graphite particles to the washed acid intercalatedgraphite particles;

(ix) a collecting vessel for collecting washed acid intercalatedgraphite particles admixed with pollution reducing chemicals;

(x) conduit means extending from said drying chamber to said collectingvessel for passing acid intercalated graphite particles admixed withacid additives from said drying chamber to said collecting vessel;

(xi) a third additive containing vessel communicating with said conduitof (x) for the introduction of ceramic fiber particles in the form ofmacerated quartz glass fibers, carbon and graphite fibers, zirconia,boron nitride, silicon carbide and magnesia fibers, naturally occurringmineral fibers such as calcium metasilicate fibers, calcium aluminumsilicate fibers, aluminum oxide fibers and the like into said conduitand the admixing and entrainment thereof with acid intercalated graphiteparticles passing from the washing vessel to the drying chamber;

(xii) an expansion chamber enclosing an open flame at a temperature of800 to 1300° C.;

(xiii) conduit means extending from said collecting vessel to saidexpansion chamber for passing dried acid intercalated graphite particlesadmixed with ceramic particles to said expansion chamber;

(xiv) gas inlet means communicating with the conduit means of (xii) forentraining the acid intercalated graphite particles admixed with ceramicparticles in a stream of non-reactive gas and passing the entrained acidintercalated graphite particles admixed with ceramic particles into theopen flame enclosed in said expansion chamber to cause expansion of theacid intercalated graphite particles of at least about 80 times to formvermiform elongated graphite particles;

(xv) a collecting hopper for receiving said vermiform elongated graphiteparticles admixed with ceramic particles;

(xvi) a separator vessel interposed between the expansion chamber andthe collecting hopper to collect by gravity separation heavy solidmineral impurity particles from the mixture of vermiform graphiteparticles with ceramic particles;

(xvii) a gas scrubber communicating with said collecting hopper tocollect gases generated in the expansion chamber;

(xviii) a compression chamber positioned to receive vermiform graphiteparticles mixed with ceramic fiber particles for compressing saidvermiform particles mixed with ceramic particles into a coherentself-supporting mat of flexible graphite from about 1 to about 0.015inches in thickness and having a density of from about 5 to about 25lbs./ft.³;

(xix) an impregnation chamber for contacting the flexible graphite matof (xviii) with liquid resin and impregnating said flexible graphitewith liquid resin;

(xx) a dryer disposed to receive the impregnated flexible graphite matof (xix) and heat and dry said mat;

(xxi) a calender mill disposed to receive the flexible graphite mat of(xix) for increasing the density of said flexible graphite mat to form acontinuous flexible graphite sheet having a density of from about 5 toabout 80 lbs/ft³, a thickness of from about 0.5 to about 0.005 inchesand relatively evenly spaced apart opposite surfaces;

(xxii) a device for mechanically deforming a surface of the continuousflexible graphite sheet of (xxi) to provide a series of repeatingpatterns on said surface flexible graphite sheet or the removal ofmaterial from said flexible graphite sheet in a series of repeatingpatterns; and

(xxiii) an oven for receiving the mat from the dryer of (xxii) to curethe resin the mat.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 1(A) show the making of a mass of un-aligned expanded graphiteparticles;

FIGS. 2, 2(A) show planar bodies of flexible graphite having portions ofun-aligned graphite particles;

FIG. 3 shows a planar body of flexible graphite that does not haveportions of un-aligned graphite particles;

FIG. 4 is a photograph (original magnification 100×) of a planar body offlexible graphite that corresponds to the sketch of FIG. 2;

FIG. 5 shows a system for the continuous production of mechanicallydeformed planar flexible graphite articles;

FIGS. 5(A) and 5(B) show different types of the flexible graphitearticles noted above; and

FIGS. 5(C) and 5(D) show conventional mechanisms for producing differenttypes of flexible graphite articles noted above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Graphite is a crystalline form of carbon comprising atoms covalentlybonded in flat layered planes with weaker bonds between the planes. Bytreating particles of graphite, such as natural graphite flake, with anintercalant of, e.g., a solution of sulfuric and nitric acid, thecrystal structure of the graphite reacts to form a compound of graphiteand the intercalant. The treated particles of graphite are oftenreferred to as “particles of intercalated graphite.” Upon exposure tohigh temperature, the particles of intercalated graphite expand indimension as much as about 80 or more times its original volume in anaccordion-like fashion in the “c” direction, i.e., in the directionperpendicular to the crystalline planes of the graphite. The exfoliatedgraphite particles are vermiform in appearance, and are thereforecommonly referred to as worms. The worms may be compressed together intoflexible sheets that, unlike the original graphite flakes, can be formedand cut into various shapes.

A common method for manufacturing graphite sheet or foil is described byShane et al. in U.S. Pat. No. 3,404,061, the disclosure of which isincorporated herein by reference. In the typical practice of the Shaneet al. method, natural graphite flakes are intercalated by dispersingthe flakes in a solution containing an oxidizing agent of, for instance,a mixture of nitric and sulfuric acid. The intercalation solutioncontains oxidizing and other intercalating agents known in the art.Examples include those containing oxidizing agents and oxidizingmixtures, such as solutions containing nitric acid, potassium chlorate,chromic acid, potassium permanganate, potassium chromate, potassiumdichromate, perchloric acid, and the like, or mixtures, such as forexample, concentrated nitric acid and chlorate, chromic acid andphosphoric acid, sulfuric acid and nitric acid, or mixtures of a strongorganic acid, e.g. trifluoroacetic acid, and a strong oxidizing agentsoluble in the organic acid.

In a preferred embodiment, the intercalating agent is a solution of amixture of sulfuric acid, or sulfuric acid and phosphoric acid, and anoxidizing agent like nitric acid, perchloric acid, chromic acid,potassium permanganate, hydrogen peroxide, iodic or periodic acids, orthe like. Although less preferred, the intercalation solutions maycontain metal halides such as ferric chloride, and ferric chloride mixedwith sulfuric acid, or a halide, such as bromine as a solution ofbromine and sulfuric acid or bromine in an organic solvent.

After the flakes are intercalated, any excess solution is drained fromthe flakes and the flakes are water-washed. The quantity ofintercalation solution retained on the flakes after draining may rangefrom 20 to 150 parts of solution by weight per 100 parts by weight ofgraphite flakes (pph) and more typically about 50 to 120 pph.Alternatively, the quantity of the intercalation solution may be limitedto between 10 to 50 parts of solution per hundred parts of graphite byweight (pph) which permits the washing step to be eliminated as taughtand described in U.S. Pat. No. 4,895,713, the disclosure of which isalso herein incorporated by reference.

Referring now to FIG. 1, intercalated graphite flakes are advantageouslyexfoliated into flexible graphite particles by passing a stream ofintercalated graphite flakes 2 through a flame 3 for only a few secondsat temperature up to or greater than 700° C., more typically 1000° C. orhigher, to exfoliate, i.e. expand the particles, and a resulting streamof expanded graphite particles, or worms 5, are passed to the top 6 of alarge open-topped vessel 7 into which the particles fall freely and arerandomly dispersed. From about 1-30% by weight of ceramic additives,indicated at 4, can be blended with the intercalated graphite flakes 2to provide enhanced properties in the final flexible graphite product.The additives include ceramic fiber particles having a length of 0.15 to1.5 millimeters. The width of the particles is suitably from 0.04 to0.004 mm. The ceramic fiber particles are non-reactive and non-adheringto graphite and are stable at temperatures up to 2000° F., preferably2500° F. Suitable ceramic fiber particles are formed of macerated quartzglass fibers, carbon and graphite fibers, zirconia, boron nitride,silicon carbide and magnesia fibers, naturally occurring mineral fiberssuch as calcium metasilicate fibers, calcium aluminum silicate fibers,aluminum oxide fibers and the like.

The dispersed expanded particles 5, with optional additive 4, arecollected and confined in the large open-topped vessel as a layer 8 ofpre-determined depth “d” and are to a large extent omnidirectionallyoriented, with some horizontally aligned, as shown at 50 in FIG. 1(A),and many extending in other directions, including vertically as shown at500 in FIG. 1(A), and in various directions other than vertical orhorizontal as shown as 5000 in FIG. 1(A). The large open-topped vesselused to collect the omnidirectionally oriented particles can be in theform of a mold as shown at 7 shaped to receive a die 9 which is used tocompress the layer 8 of omnidirectionally oriented exfoliated graphiteparticles 50, 500, 5000 to a density of from about 0.1 to 25 pounds percubic foot at a thickness of from 25 to 0.15 inches. Under theseconditions, the omnidirectional orientation of the exfoliated acidtreated graphite is conserved to a substantial extent in the compressedplanar flexible graphite article 100, having parallel opposed faces ormajor surfaces 101, 103, as shown in the sketch of the edge of theplanar article illustrated in FIG. 2 and is also conserved when thematerial of FIG. 2 is pressed into sheet having a density of 25 to 100pounds per cubic foot and a thickness of 0.15 to 0.04 inch as shown inthe similar sketch of FIG. 2(A).

The use of continuous converging opposing belts, as shown at 457, 458 inFIG. 5, such as porous belts converging from a spacing of 25 inches to aspacing of 0.15 inch over a length of 8 to 12 feet, approximates theaction of a mold and die with longer lengths, more than 8 feet providingincreased conservation of omnidirectional orientation. A prior arthighly densified sheet 200 of directly roll pressed intercalated acidtreated graphite is illustrated in the sketch of FIG. 3 which shows theorientation of the exfoliated, expanded graphite particles 210 to besubstantially parallel to the major opposed parallel surfaces 301, 303of the planar sheet 200. FIG. 4 is a photograph of the edge of acompressed (100 lb./cu. ft.) planar article in accordance with thepresent invention corresponding generally to the sketch of FIG. 2 withthe omnidirectionally oriented exfoliated, expanded graphite particlesbeing correspondingly indicated at 50, 500, 5000.

The article of FIG. 3 is highly anisotropic with respect to thermal andelectrical conductivity; the articles of FIGS. 2, 2(A) and 4 exhibitenhanced isotropy with respect to thermal and electrical conductivity,as compared to the article of FIG. 3.

The articles of FIGS. 2, 2(A) and the material shown in the photograph(100×) of FIG. 4 can be shown to have increased thermal and electricalconductivity in the direction transverse to opposed planar surfaces 101,103 as compared to the thermal and electrical conductivity in thedirection transverse to surfaces 301, 303 of prior art material of FIG.3 in which particles of expanded natural graphite unaligned with theopposed planar surfaces are not optically detectable.

With reference to FIG. 5, a system is disclosed for the continuousproduction of roll-pressed flexible graphite sheet. In the inventivesystem, graphite flakes and a liquid intercalating agent are chargedinto reactor 404. More particularly, a vessel 401 is provided forcontaining a liquid intercalating agent. Vessel 401, suitably made ofstainless steel, can be continually replenished with liquid intercalantby way of conduit 406. Vessel 402 contains graphite flakes that,together with intercalating agents from vessel 401, are introduced intoreactor 404. The respective rates of input into reactor 404 ofintercalating agent and graphite flake are controlled, such as by valves408, 407. Graphite flake in vessel 402 can be continually replenished byway of conduit 409. Additives, such as intercalation enhancers, e.g.,trace acids, and organic chemicals may be added by way of dispenser 410that is metered at its output by valve 411.

The graphite flakes in reactor vessel 404 are subjected to interlayerattack by the acid mixture intercalant, as described in U.S. Pat. No.3,404,061 to Shane et al. The resulting intercalated graphite particlesare soggy and acid coated and are conducted (such as via conduit 412) toa wash tank 414 where the particles are washed, advantageously withwater which enters and exits wash tank 414 at 416, 418. The washedintercalated graphite flakes are then passed to drying chamber 422 suchas through conduit 420. Additives such as buffers, antioxidants,pollution reducing chemicals can be added from vessel 419 to the flow ofintercalated graphite flake for the purpose of modifying the surfacechemistry of the exfoliate during expansion and use and modifying thegaseous emissions which cause the expansion.

The intercalated graphite flake is dried in dryer 422, preferably attemperatures of about 75 to about 150° C., generally avoiding anyintumescence or expansion of the intercalated graphite flakes. Afterdrying, the intercalated graphite flakes are fed as a stream into flame300, by, for instance, being continually fed to collecting vessel 424 byway of conduit 426 and then fed as a stream into flame 300 in expansionvessel 428 as indicated at 2. Additives such as ceramic fiber particlesformed of macerated quartz glass fibers, carbon and graphite fibers,zirconia, boron nitride, silicon carbide and magnesia fibers, naturallyoccurring mineral fibers such as calcium metasilicate fibers, calciumaluminum silicate fibers, aluminum oxide fibers and the like can beadded from vessel 429 to the stream of intercalated graphite particlespropelled by entrainment in a non-reactive gas introduced at 427.

The intercalated graphite particles 2, upon passage through flame 300 inexpansion chamber 301, expand more than 80 times in the “c” directionand assume a “worm-like” expanded form; the additives introduced from429 and blended with the stream of intercalated graphite particles areessentially unaffected by passage through the flame 300. The expandedgraphite particles may pass through a gravity separator 430, in whichheavy ash natural mineral particles are separated from the expandedgraphite particles, and then into a wide topped hopper 432. Separator430 can be by-passed when not needed.

The expanded, i.e., exfoliated graphite particles fall freely in hopper432 together with any additives, and are randomly dispersed and passedinto compression station 436, such as through trough 434. Compressionstation 436 comprises opposed, converging, moving porous belts 457, 458spaced apart to receive the exfoliated, expanded graphite particles 50,500, 5000. Due to the decreasing space between opposed moving belts 457,458, the exfoliated expanded graphite particles are compressed into amat of flexible graphite, indicated at 448 having thickness of, e.g.,from about 1.0 to 0.003, especially from about 1.0 to 0.1 inches, and adensity of from about 5 to 125 lbs./ft³. Gas scrubber 449 may be used toremove and clean gases emanating from the expansion chamber 301 andhopper 432.

The mat 448 is passed through vessel 450 and is impregnated with liquidresin from spray nozzles 438, the resin advantageously being “pulledthrough the mat” by means of vacuum chamber 439 and the resin isthereafter preferably dried in dryer 460 reducing the tack of the resinand the resin impregnated mat 443 is thereafter densified into rollpressed flexible graphite sheet 447 in calender mill 470. Gases andfumes from vessel 450 and dryer 460 are preferably collected and cleanedin scrubber 465.

The calendered flexible graphite sheet 447 is passed through surfaceshaping unit 480 and is mechanically deformed at its surface byembossing die stamping or the like, and thereafter heated in oven 490 tocure the resin, to continuously provide a flexible graphite sheet 444 ofrepeated surface altered patterns such as the grooved patterns 600 shownin FIG. 5A, which can be cut to provide flexible graphite components 650of a fuel cell such as fluid flow plate shown at 650 in FIG. 6A orgaskets 750 as shown at 700 in FIG. 5B.

Depending on the nature of the resin system employed, and especially thesolvent type and level employed, a vaporization drying step may beincluded prior to the surface shaping (such as embossing) step. In thisdrying step, the resin impregnated flexible graphite sheet is exposed toheat to vaporize and thereby remove some or all of the solvent, withouteffecting cure of the resin system. In this way, blistering during thecuring step, which can be caused by vaopization of solvent trappedwithin the sheet by the densification of the sheet during surfaceshaping, is avoided. The degree and time of heating will vary with thenature and amount of solvent, and is preferably at a temperature of atleast about 90° C. and more preferably from about 90° C. to about 125°C. for about 3 to about 20 minutes for this purpose.

The above description is intended to enable the person skilled in theart to practice the invention. It is not intended to detail all of thepossible variations and modifications which will become apparent to theskilled worker upon reading the description. It is intended, however,that all such modifications and variations be included within the scopeof the invention which is defined by the following claims. The claimsare intended to cover the indicated elements and steps in anyarrangement or sequence which is effective to meet the objectivesintended for the invention, unless the context specifically indicatesthe contrary.

1. A system for the continuous production of surface patterned,resin-impregnated flexible graphite sheet which comprises: (i) a reactorvessel for containing as reactants raw natural graphite particles inmixture with sulfuric and nitric acids; (ii) an acid containing vesselcommunicating with said reactor vessel for the introduction of a mixtureof sulfuric and nitric acid into said reactor vessel; (iii) a graphiteparticle containing vessel for the introduction of graphite particlesinto the reactor vessel; (iv) a first additive containing vesselcommunicating with said reactor vessel for the introduction ofintercalation enhancing materials, acids or organic chemicals; (v) awash vessel containing water communicating with the reactor vessel toreceive reaction product in the form of acid intercalated graphiteparticles and remove acid from the surface of the acid intercalatedgraphite particles and a portion of the mineral impurities contained inthe natural graphite particles introduced into the reactor vessel; (vi)a drying chamber for drying washed acid intercalated graphite particles;(vii) conduit means extending from said wash vessel to said dryingchamber for passing washed acid intercalated graphite particles from thewash vessel to the drying chamber; (viii) an expansion chamber enclosingan open flame at a temperature of at least about 700° C.; (ix) conduitmeans extending from said collecting vessel to said expansion chamberfor passing dried acid intercalated graphite particles to said expansionchamber; (x) gas inlet means communicating with the conduit means of(viii) for entraining the acid intercalated graphite particles in astream of non-reactive gas and passing the entrained acid intercalatedgraphite particles into the open flame enclosed in said expansionchamber to cause expansion of the acid intercalated graphite particlesto form vermiform elongated graphite particles; (xi) a collecting hopperfor receiving said vermiform elongated graphite particles; (xii) acompression chamber positioned to receive vermiform graphite particlesfor compressing said vermiform particles into a coherent self-supportingmat of flexible graphite; (xiii) an impregnation chamber for contactingthe flexible graphite mat of (xviii) with resin and impregnating saidflexible graphite with resin; (xiv) a calender mill disposed to receivethe flexible graphite mat for increasing the density of said flexiblegraphite mat to form a continuous flexible graphite sheet; (xv) a devicefor mechanically deforming a surface of the continuous flexible graphitesheet of (xiv) to provide a series of repeating patterns on said surfaceflexible graphite sheet or the removal of material from said flexiblegraphite sheet in a series of repeating patterns; and (xvi) an oven forreceiving the mat from the dryer of (xv) to cure the resin.